1. Field of the Invention
The present invention relates to a process for the preparation of a semiconductor device. More particularly, the present invention relates to a process for the preparation of a semiconductor device, in which a dry etching of a laminated film consisting of a metal silicide silicon layer and non-single crystalline layer is employed.
2. Description of the Related Art
In the field of the production of semiconductor devices, the recent increase of the degree of integration and density of ICs, has led to the need for a fine processing technique to cope with this increase. Under these circumstances, a laminated film consisting of a metal silicide layer having an electrical resistivity and a polysilicon layer has been widely used. When etching this film, a dry etching method is employed in which SF.sub.6 and CCl.sub.4 are used as an etching gas.
In the past method, however, an undercutting is apt to be formed in the etched pattern, and thus the accuracy of the pattern dimensions is low, and further, the selectivity of a polycrystalline silicon to a silicon dioxide is low. Accordingly, it has become necessary to develop a fine-pattern forming technique by which the above problems are solved and a fine patterning obtained.
To date, the following publications are known which disclose a dry etching method by which a laminated film consisting of a metal silicide layer and a polycrystalline silicon is etched.
(A) A dry etching by a mixed gas of SF.sub.6 and O.sub.2 : [Reference: polycide-structure etching by an SF.sub.6 glow discharge, using a low cycle excitation parallel flat-type reactor: M. E. Coe. S. H. Rogers: solid state technology (Japanese edition) 1982];
(B) Two-step etching consisting of a first reactive ion etching using a fluorine-contained gas, for a metal silicide, and a second reactive ion etching using a chlorine-type gas, for a polycrystalline silicon (Japanese Examine Patent Publication (Kokoku) No. 61-168228 filed by Sharp K. K.); and
(C) A dry etching using a mixed gas Cl.sub.2 and BCl.sub.3, for a double film consisting of a metal silicide layer and a polycrystalline silicon (Japanese patent application No. 59-85051).
Also, the following publications disclose a method of dry etching a single film of a metallic layer having a high melting point, or a metal silicide layer having a high melting point.
(D) A reactive ion etching using a mixed gas of Cl.sub.2 and O.sub.2 for a metal silicide single layer (Japanese examined patent publication (Kokoku) No. 60-064476, filed by Fujitsu Co., Ltd.; Japanese examined patent publication (Kokoku) No. 01-243430, by Nippon Electric Co., Ltd.; and Japanese examined patent publication (Kokoku) No. 02-094520, filed by Nippon Electric Co., Ltd.).
In the above method (A) it is impossible to obtain a vertical patterning due to large undercutting remaining in the etched pattern.
In the above method (B), SF.sub.6 gas and CCl.sub.4 gas are used for the first etching step, and CCl.sub.4 gas and O.sub.2 gas are used for the second etching step. Nevertheless, it is impossible to obtain a vertical pattern even though the amount of undercutting is reduced to a certain extent. Furthermore, the selectivity to the silicon dioxide in the first etching step is low, e.g., 1 to 2, and the selectivity in the second etching step is also low, e.g., 2 to 3.
Also, differences exist between the patterning profile obtained at the area wherein the space to be etched per unit space is large (hereinafter called the coarse area), and the area wherein the space to be etched per unit space is small (hereinafter called the thick area).
Therefore, this method is not suitable for the preparation of the semiconductor device having both coarse and thick portions. Furthermore, use of the CCl.sub.4 gas is now banned under environmental protection laws, e.g., the Freon-control law.
In the above method (C), BCl.sub.3 gas which is apt to form by-products, i.e., deposits, and is called a deposition gas, was successfully employed to form a vertical pattern in which the laminated film is protected by a side wall. Nevertheless, a small amount of BCl.sub.3 gas causes a change of the etching rate, and accordingly, the pattern is not uniform in the field of the substrate, and thus the reproducibility is bad due to the influence of the BCl.sub.3 deposited in the etching reaction chamber. Also, because BCl.sub.3 is a deposition gas, a gas flow meter becomes clogged and the particles are deposited in the etching reaction chamber. A similar problem arises if the BCl.sub.3 is replaced by SiCl.sub.4.
In the above method (D), the laminated film consisting of the metal silicide layer and the polycrystalline film is etched, but a vertical side is not obtained, and accordingly, the etching rate of the upper metal silicide layer is faster than that of the lower polycrystalline silicon layer. Also, the uniformity of the etching rate of the metal silicide layer is bad, and thus the obtained pattern is not uniform in the substrate.
Under these circumstances, there is a need to develop a dry etching technique by which the laminated film consisting of the metal silicide compound layer and the polycrystalline silicon layer can be fabricated to form a vertical side in profile without employing a gas which can not be permitted to be used under the Freon Regulations and a deposition gas, and by employing this technique a fine pattern can be obtained without an edge profile between the coarse area and the thick area of the pattern, and in the substrate, while having a high selectivity to the lower silicon dioxide layer.